Asphalt or bitumen is a mixture of various hydrocarbons and contains varying amounts of paraffinic, naphthenic, and aromatic hydrocarbons. It has properties which make it useful in a number of applications including as a surface application to a road bed or road surface, a sealing compound, a coating material, a waterproofing material. It may also be used to protect building structures or components of building structures, and as a caulking or waterproofing material.
Neat bitumen generally has little or no elasticity. Thus, asphalt processing is difficult and resultant coatings or pavement layers comprised of bitumen are brittle at low temperatures and soft at higher temperatures. Numerous products have been developed in an attempt to modify the bitumen and provide it with elasticity, reduced brittleness and increased processability. Such attempts include blending the bitumen with amounts of various polymers, most commonly SBS. The objective of using polymers as bitumen additives is to alter the viscoelastic properties of bitumen, in particular to extend the plasticity range and to improve the elastic restoration. These materials are commonly referred to as “polymer modified bitumens” (PMBs).
The process of preparing PMBs requires heating and shear mixing of the polymer and the bitumen which give the high viscosity of the bitumen, requires application of significant shear rates, relatively high temperatures in the reactors, and longer processing times.
While PMBs have been considered an improvement over neat bitumens, the end products still lack sufficient flexibility, particularly at lower temperatures (such as those present during most road maintenance operations). Moreover, the difficulties associated with the processing of PMB remain a challenge.
U.S. Pat. No. 4,902,349 to Wakizaka describes the difficulties associated with the mixing of asphalt and a polyol, reporting that asphalt separates from the polyol because of poor compatibility. To overcome this difficulty, Wakizaka uses high levels of polyol (40% by weight or greater) and requires use of a surface active agent and a plasticizer. Wakizaka teaches that its composition is prepared by “utilizing the behavior of a plasticizer according to the polymer solution theory and the surface-modifying effect of the plasticizer according to surface chemistry.” The Wakizaka method and composition are flawed and commercial infeasible because of the costs added by use of the large amount of polyol and the additional required ingredients. There remains a need in the art for a lower cost flexible asphalt that can be used commercially in large quantities without being cost prohibitive.